A method of using a fuel vapor pressure management apparatus to manage pressure and detect leaks in a fuel system. In particular, a method of using a fuel vapor pressure management apparatus to vent positive pressure, vent excess negative pressure, and use naturally forming vacuum to perform a leak diagnostic.
Conventional fuel systems for vehicles with internal combustion engines can include a canister that accumulates fuel vapor from a headspace of a fuel tank. If there is a leak in the fuel tank, the canister, or any other component of the fuel system, fuel vapor could escape through the leak and be released into the atmosphere instead of being accumulated in the canister. Various government regulatory agencies, e.g., the California Air Resources Board, have also promulgated standards related to limiting fuel vapor releases into the atmosphere. Thus, it is believed that there is a need to avoid releasing fuel vapors into the atmosphere, and to provide an apparatus and a method for performing a leak diagnostic, so as to comply with these standards.
In such conventional fuel systems, excess fuel vapor can accumulate immediately after engine shutdown, thereby creating a positive pressure in the fuel vapor pressure management system. Excess negative pressure in closed fuel systems can occur under some operating and atmospheric conditions, thereby causing stress on components of these fuel systems. Thus, it is believed that there is a need to vent, or xe2x80x9cblow-off,xe2x80x9d the positive pressure, and to vent, or xe2x80x9crelieve,xe2x80x9d the excess negative pressure. Similarly, it is also believed to be desirable to relieve excess positive pressure that can occur during tank refueling. Thus, it is believed that there is a need to allow air, but not fuel vapor, to exit the tank at high flow rates during tank refueling. This is commonly referred to as onboard refueling vapor recovery (ORVR).
The present invention provides a method of managing fuel vapor pressure in a fuel system. The method includes locating between first and second ports a poppet and a seal cooperating with the poppet, positioning the seal in a substantially symmetrically deformed configuration so as to sense a negative pressure at a first pressure level, positioning the seal in a generally asymmetrically deformed configuration so as to vent negative pressure below the first pressure level, and positioning the seal in an undeformed configuration so as to vent positive pressure above a second pressure level. The poppet is movable along an axis. And the seal is flexible between the undeformed configuration when disengaged from the poppet, the substantially symmetrically deformed configuration when engaged with the poppet, and the generally asymmetrically deformed configuration when engaged with the poppet.